Many display systems use multiple spatial light modulators, such as liquid crystal display panels (LCD's) or digital micromirror devices (DMD™) to create a single full color image. Generally, a white light source is used to create a white light beam that is split, using dichoric filters, into three primary color light beams. Each primary color light beam is incident on a separate modulator and the three modulated primary color light beams are recombined to form a single full color image on a display surface.
However, as will be appreciated by those skilled in the art, color splitting/combining prisms as typically used with spatial light modulators have equal glass path lengths through the prism system in order to promote lens design symmetry and picture quality. Further, the size of the prism arrangement is determined by optimizing the dichoric angles for the desired color with matching path lengths and then scaling the overall size of the prism to fit the size of the device being imaged. Since the red channel typically has the narrowest clear aperture, it is typically the red channel therefore that determines or sets the overall size of the prism arrangement that will be required for a particular image size. Once the size of the prism arrangement is set as required by the red channel, it will be appreciated that the blue and green channels will have larger clear apertures than that of the red channel and could handle larger images. Unfortunately, an acceptable image cannot be generated if the image size of the red channel is different than that of the green and blue channels.
Therefore, if the red channel clear aperture could be increased to be as large or equal to the clear aperture available with the blue and green channels, optimally sized prism arrangements with minimal glass content and, consequently, minimal cost, could be appreciated.